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Good day to all!

I am planning on designing an electric vehicle architecture from scratch. My main DC bus voltage is 400 V. However, I have got different voltages in my system. I have got a 600/400 V buck converter to supply my air conditioning compressor and I have got a motor inverter that outputs 3 phase AC supply.

To make myself clear, I am attaching an image of my high voltage junction box. enter image description here

With this architecture, I have a confusion about monitoring the insulation resistance of my high voltage bus. I am currently planning to keep an insulation monitoring device (IMD) from Bender (Isometer IR155-3203).

I would like to know whether I need separate IMDs for my 400 V supply to the air conditioning as well as the 3 phase AC supply to my motor. Do I need to be concerned about multiple voltages in the same system? If not, what can I do detect a break in the insulation at any point in my HV bus? I hope my question makes sense, if it doesn't please let me know.

PS: The image is just for representation. Please let me know if you need more details.

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    \$\begingroup\$ Your insulation resistance of the whole system typically needs to be >10 MOhm regardless of the voltage level. Is your buck isolated? \$\endgroup\$
    – F. Heisenberg
    Commented Apr 18, 2022 at 12:03
  • \$\begingroup\$ Yes, my buck is isolated. \$\endgroup\$
    – gr3en_apple
    Commented Apr 18, 2022 at 12:46

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DISCLAIMER

Advice given here carries no legal weight and should not be relied on to avoid causing injury or death.

The most advisable path would be to ask the manufacturer.
They say:

  • "The patented measurement technology is used to monitor the condition of the insulation on the DC side as well as on the AC motor side of the electrical drive system."

Unless you wish to analyse the patent document and are confident in your competence in doing so, trying to work out what a "patented measurement technology" may do is risky. Only manufacturer's advice or real world user experience will help - and the latter is really only useful if someone can definitively state it always works and why.

That said, I'd expect that they detect any DC bus leakage to ground whether it occurs before or after the AC drive. I'd expect that if the buck converter is effectively DC continuous from input to output (as many but not all are) then it would 'probably' work and of the converter was isolated it would be much less likely to. It would be trivially easy to test by (suitably safe) experiment.

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  • \$\begingroup\$ Hi Thank you for your inputs! Does isolation affect the insulation monitoring process? What if my inverter is also isolated? And YES, I will contact the manufacturer and confirm the same. But right now, I am in the design phase and performing a cost estimate on what all components I would require. \$\endgroup\$
    – gr3en_apple
    Commented Apr 18, 2022 at 12:48
  • \$\begingroup\$ @gr3en_apple As above, whether it works with isolation depends on "The patented measurement technology" - I imagine that you can't be certain BUT if I had to guess I'd say that isolation would make things much harder UNLESS they had sensors attached to the isolated side(s). \$\endgroup\$
    – Russell McMahon ♦
    Commented Apr 20, 2022 at 10:08
  • \$\begingroup\$ Alright, thanks a lot. It helps. \$\endgroup\$
    – gr3en_apple
    Commented Apr 26, 2022 at 9:07

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